Opposed piston, two-stroke cycle diesel engines have been in development for a number of years. Theoretically, due to its configuration, an opposed piston, two-stroke cycle diesel engine should generate more power than a comparable sized four-stroke diesel engine. This is so because the two-stroke cycle engine has twice as many power cycles per revolution as does the four-stroke cycle engine.
In order to maximize the benefit of an opposed piston, two-stroke cycle diesel engine, it is desirable to make the engine as compact as possible. As a high output engine is made very compact, however, cooling becomes difficult and can pose serious concerns. This happens because an excessive amount of heat is generated within a confined area, and there is very little room in this confined area for coolant to pass through the engine. Furthermore, if the cooling system design is compromised as a trade-off to compactness, uneven cooling or inadequate cooling can result and lead to premature failure of the engine.
In order to maximize thermal efficiency, in addition to effective cooling, it is also desirable to reduce heat transfer and thereby retain as much heat as possible in the exhaust stream. This is particularly desirable when heat in the exhaust stream can be subsequently used to maximize turbocharger output. The reduction of heat transfer is more difficult in the opposed piston engine than in the more conventional four-stroke engine because the exhaust ports are located all around the cylinder chamber. The exhaust gases must therefore be redirected in order to exit the engine block on the sides. Redirecting the flow without some means of minimizing heat transfer, however, will increase the cooling problem previously mentioned and simultaneously reduce the amount of heat retained for transfer to the turbocharger.
It is also of some concern that, present opposed piston, two-stroke diesel engines suffer from incomplete fuel combustion within the cylinder chamber. Because of the opposed piston design, the fuel injector is not able to inject the combustion fuel to the top center of the pistons. Instead, the fuel injectors must inject from a cylinder wall. Presently, existing designs are not able to effectively mix and/or distribute the fuel within the cylinder chamber. Frequently, in order to improve the fuel combustion, some existing diesel two-stroke engines are initiating a strong swirl within the cylinder chamber to enhance the removal of the exhaust fluid from the cylinder chamber. However, the strong swirl can subsequently inhibit the propagation of the diesel within the cylinder chamber and cause incomplete fuel combustion within the cylinder chamber. This has minimized the efficiency of these engines.
In light of the above, it is an object of the present invention to provide an opposed piston, two-stroke cycle diesel engine which operates more efficiently, is more durable and is more reliable than existing engines. Another object of the present invention is to provide an opposed piston, two-stroke cycle diesel engine having an improved cooling system and thermal shields which allow the engine to operate at a cooler temperature. Still another object of the present invention is to provide a two-stroke diesel engine having improved fuel ignition and combustion characteristics.